Cutting insert and tool for machining a workpiece

ABSTRACT

A cutting insert for a tool for machining a workpiece, wherein the cutting insert has a 180° rotational symmetry about a bore axis extending perpendicularly and centrally through two opposing, identical base surfaces of the cutting insert, and has two identical parts which are connected along a center plane, wherein said center plane extends orthogonally to the bore axis and has the same distance from each of the two base surfaces, wherein each part has two identical mutually opposite main sides and two identical mutually opposite secondary sides, wherein each main side has a rectilinear main cutting edge extending parallel to the center plane, and each secondary side has a planar bearing surface extending orthogonally to the center plane, wherein the two main cutting edges of each part extend parallel to one another and transversely to the two main cutting edges of the respective other part, and wherein the two main cutting edges of each part extend parallel to the two bearing surfaces of the respective other part, wherein each main cutting edge transitions at its respective first end into a first segmental cutting edge which is arranged on a first protrusion provided on an adjacent secondary side of the respective part, and wherein each main cutting edge transitions into a second segmental cutting edge at its respective second end, opposite the first end, which is arranged on a second protrusion provided on the respective other adjacent secondary side of the respective part, wherein the first and the second protrusions each adjoin the bearing surface arranged on the respective same secondary side and project with respect to the respective bearing surface.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of international patent applicationPCT/EP2013/068089, filed on Sep. 2, 2013 designating the U.S., whichinternational patent application has been published in German languageand claims priority from German patent application DE 10 2012 108 752.0,filed on Sep. 18, 2012. The entire contents of these priorityapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This disclosure relates to a cutting insert, in particular a tangentialcutting insert, for a tool for machining a workpiece. Furthermore, thedisclosure relates to a tool for machining a workpiece, in particularfor tangential milling, having a tool holder which has at least onecutting-insert receptacle in which a cutting insert according to thepresent disclosure is releasably fastened.

Cutting inserts of the present type, which are generally denotedindexable cutting inserts or in particular as tangential cuttinginserts, are usually used in applications for metalworking, inparticular in milling or turning applications. Primarily, the presentcutting inserts are used for tangential milling. Milling tools in whichsuch cutting inserts are used typically comprise a rotationallysymmetrical tool holder on the circumference of which at least one, butusually a multiplicity of said cutting inserts are releasably fastened.

The removal of material from the workpiece during the milling operationis ensured by high-precision blade edges or cutting edges which areformed in the cutting inserts. In order to keep the wear as low aspossible, to withstand the very high cutting forces that arise duringprocessing and to ensure precision that is as high as possible, thesecutting inserts are usually produced from carbide. Nevertheless, onaccount of the high material stress, the cutting edges become worn overtime. Therefore, in particular for milling operations which require highprecision, the cutting inserts have to be replaced after a particularperiod of time.

In order to prevent the relatively expensive cutting inserts from havingto be replaced in their entirety each time the cutting edges becomeworn, multisided cutting inserts which have a plurality of cutting edgesthat are arranged in a symmetrical manner with respect to one anotherhave been developed. Such an indexable cutting insert having fouridentical main cutting edges that are arranged in a symmetrical mannerwith respect to one another is known for example from EP 1 572 407 B1.

The indexable cutting insert shown therein is formed so as to berotationally symmetrical through 180° with regard to each of its threemain axes. As soon as the used main cutting edge becomes worn, theindexable cutting insert can therefore be rotated and/or reversedthrough 180° and be fastened in the new position in the tool holder. Inthe event of wear to one of the four main cutting edges, the indexablecutting insert thus does not have to be replaced in its entirety butonly rotated or reversed in the holder, and so machining can becontinued with the previously unused, unworn main cutting edges.

On account of the symmetry properties of the indexable cutting insert,in which each main cutting edge has the same cutting edge geometry, thecutting properties are not changed by reversing or rotating theindexable cutting insert. In other words, one and the same indexablecutting insert can thus be used four times until all of the cuttingedges become worn and the indexable cutting insert has to be disposedof.

In contrast to simple, non-reversible cutting inserts, such indexablecutting inserts afford much greater flexibility and, since they areusable repeatedly, can be used for much longer without this beingassociated with losses in terms of machining accuracy. Although suchfour-edged indexable cutting inserts are much more complex to producethan conventional, single-edged (non-reversible) cutting inserts, theyprove to be not only more versatile but also, when considered as awhole, more cost-effective for the consumer.

However, from the point of view of the manufacturer of such indexablecutting inserts, the problem in structural terms is not only that ofrealizing the symmetry properties of such indexable cutting inserts witha plurality of identical cutting edges, but at the same time alsoensuring that each of these cutting edges has the same machiningproperties and as a result is usable in an identical manner. Thegreatest problem is in this case often that of avoiding possiblecollisions with other components of the cutting insert or of the toolholder, and of ensuring secure seating of the cutting insert in the toolreceptacle of the tool holder, so that optimal force introduction isensured.

In particular, care must be taken to ensure that the cutting edges thatare not being used at the particular time or other components of thecutting insert do not collide in an undesired manner with the workpiece.Thus, collisions with the workpiece must not occur at locations on thecutting insert which are not intended to be used for machining theworkpiece at the particular time. In other words, care must thus betaken to ensure that the cutting edges that are not being used at theparticular time run free. It stands to reason that such requirements aremore difficult to meet in the case of indexable cutting inserts having aplurality of alternately usable cutting edges than is the case forconventional cutting inserts having only one cutting edge.

The abovementioned symmetry properties, the free running of theremaining cutting edges and the avoidance of undesired collisions of thecutting insert with the workpiece is solved in the case of the indexablecutting insert known from EP 1 572 407 B1 in that the indexable cuttinginsert has two parts which are twisted through a predefined angle withrespect to one another about a main axis of the indexable cuttinginsert. The main cutting edges are in this case each twisted through apredefined angle with respect to one another. In this way, the requiredsymmetry and free-running properties can be ensured in a technicallysustainable manner. On the other hand, in the case of such an indexablecutting insert that is twisted on itself, a relatively large number ofsurfaces of complex shape arise. Such twisting results, in particular atthe main insert surfaces, in relatively complex rake faces which aretechnically very demanding to manufacture. Demanding manufacture of thistype, even if this should be technically feasible, is associated withvery high manufacturing costs. Ultimately, this results in high unitcosts of the indexable cutting inserts for the final consumer.

SUMMARY OF THE INVENTION

It is thus an object to provide a cutting insert of the type mentionedat the beginning which provides an alternative to the abovementionedindexable cutting inserts known from the prior art and in particular iseasier to produce.

In view of this object, a cutting insert is provided which comprises:

-   two identical parts, wherein each part has a base surface, two    identical mutually opposite main sides and two identical mutually    opposite secondary sides, and wherein the base surface of the one of    the two parts is opposite and parallel to the base surface of the    other one of the two parts;-   four rectilinear main cutting edges, wherein each of the two parts    comprises two of the four rectilinear main cutting edges;-   four first segmental cutting edges, wherein each of the two parts    comprises two of the four first segmental cutting edges;-   four second segmental cutting edges, wherein each of the two parts    comprises two of the four second segmental cutting edges;-   a through-bore having a bore axis which extends perpendicularly and    centrally through the two base surfaces;

wherein the cutting insert has a 180° rotational symmetry about the boreaxis, wherein the two identical parts are connected to each other alonga center plane which extends orthogonally to the bore axis and has thesame distance from each of the two base surfaces,

wherein the four main cutting edges extend parallel to the center plane,wherein each main side comprises one of the four main cutting edges,wherein the two main cutting edges of each part extend parallel to oneanother and transversely to the two main cutting edges of the respectiveother part, and wherein each main cutting edge transitions at itsrespective first end into one of the four first segmental cutting edgesand at its respective second end, opposite the first end, into one ofthe four second segmental cutting edges,wherein each secondary side comprises (i) a planar bearing surface whichextends orthogonally to the center plane, (ii) a first protrusion on afirst side of the planar bearing surface and (iii) a second protrusionon a second side of the planar bearing surface, wherein the first andthe second protrusions each adjoin the bearing surface arranged on therespective same secondary side and project with respect to said bearingsurface, wherein each of the first segmental cutting edges is arrangedon one of the first protrusions and each of the second segmental cuttingedges is arranged on one of the second protrusions, and wherein thebearing surfaces of each part extend parallel to the main cutting edgesof the respective other part.

According to a further aspect, a cutting insert is provided, wherein thecutting insert has a 180° rotational symmetry about a bore axisextending perpendicularly and centrally through two opposing, identicalbase surfaces of the cutting insert, and has two identical parts whichare connected along a center plane, wherein said center plane extendsorthogonally to the bore axis and has the same distance from each of thetwo base surfaces, wherein each part has two identical mutually oppositemain sides and two identical mutually opposite secondary sides, whereineach main side has a rectilinear main cutting edge extending parallel tothe center plane, and each secondary side has a planar bearing surfaceextending orthogonally to the center plane, wherein the two main cuttingedges of each part extend parallel to one another and transversely tothe two main cutting edges of the respective other part, and wherein thetwo main cutting edges of each part extend parallel to the two bearingsurfaces of the respective other part, wherein each main cutting edgetransitions at its respective first end into a first segmental cuttingedge which is arranged on a first protrusion provided on an adjacentsecondary side of the respective part, and wherein each main cuttingedge transitions into a second segmental cutting edge at its respectivesecond end, opposite the first end, which is arranged on a secondprotrusion provided on the respective other adjacent secondary side ofthe respective part, wherein the first and the second protrusions eachadjoin the bearing surface arranged on the respective same secondaryside and project with respect to the respective bearing surface.

The presented cutting insert is a completely novel four-edged cuttinginsert which, compared with the cutting inserts known from the priorart, is advantageous not only from a manufacturing point of view butalso on account of improved cutting properties. Although the presentedcutting insert , in a similar manner to the cutting insert known from EP1 572 407 B1, has two identical parts that are joined together and islikewise rotationally symmetrical through 180° about a bore axisextending centrally through the cutting insert, nevertheless, thepresented cutting insert cannot be compared with the cutting insertknown from EP 1 572 407 B1 either from a structural point of view orfrom a geometrical and manufacturing point of view. Both the cuttinggeometry and the bearing surfaces which are provided on the cuttinginsert and with which the cutting insert bears against the tool holderare configured in a completely different manner in the cutting insertaccording to the present disclosure. In contrast to the cutting insertknown from EP 1 572 407 B1, the cutting insert according to thisdisclosure is also not configured so as to be 180° rotationallysymmetrical about all of its main axes but only about the central boreaxis. All four identical, rectilinear main cutting edges (blade edges)that are provided on the cutting insert are nevertheless usable in anidentical manner without the machining or cutting properties changingwhen a change is made from one cutting edge to the other cutting edge.

At this point it should be noted that, within the meaning of the presentdisclosure, “180° rotationally symmetrical” means that the cuttinginsert is mapped onto itself when rotated through 180° about the boreaxis. Furthermore, it should be mentioned that the “parts” definedherein are not intended to be understood as separate components of thecutting insert that are separable from one another, but are onlyintended to signify that the cutting insert consists of two bodies thatare constructed in a geometrically identical manner and together formthe cutting insert. These two parts are connected together integrallyalong the center plane in the present case.

Each of these parts has one of the two base surfaces that extendparallel to one another and is spatially delimited on the spatial sidesextending transversely thereto by in each case two opposing main sidesand two secondary sides that are arranged transversely thereto and arelikewise opposite one another. Main and secondary sides thus eachdesignate two opposite spatial sides of the respective part, which,together with the base surface, delimit the surface of each part.

Each of these two main sides per part or a total of four main sides ofthe cutting insert have a main cutting edge which is arranged thereon,extends in a rectilinear and parallel manner to the center plane and theends of which are each adjoined by a first and a second segmentalcutting edge. The expressions “first segmental cutting edge” and “secondsegmental cutting edge” should be understood in each case only asdesignations for different segmental cutting edges of the cuttinginsert, that is to say not as a numerical limitation. Accordingly, thecutting insert has as a whole not only four main cutting edges but alsofour first segmental cutting edges and four second segmental cuttingedges. The first and second segmental cutting edges are in the presentcase only kept apart on account of the geometrical and size differencesbetween one another. The first and second segmental cutting edges arearranged at the eight spatially external corners of the cutting insert.According to a refinement, the first and second segmental cutting edgesare each configured as a corner radius or bevel. Since the workpiece canbe machined with these corner radii or corner bevels as well, these aredesignated first and second segmental cutting edges in the present case.

An essential feature of the herein presented cutting insert can be seenin the fact that the mentioned first and second segmental cutting edgesare arranged at the first and second protrusions provided on eachsecondary side of each part. The designations “first protrusions” and“second protrusions” should in this case in turn be regarded merely asthe names or definitions for protrusions that are each the same shape orthe same size, or as distinguishing terms for two different types ofprotrusions, namely first and second protrusions, which are arranged onthe secondary sides of each part in the region of the corners of thecutting insert. In the present case, in each case one first protrusionand in each case one second protrusion adjoin the end of the planarbearing surface arranged on the same secondary side, and project withrespect thereto. The first and second protrusions are thus understood asbeing material protrusions or material elevations which are arranged onthe secondary sides of each part, respectively, and project laterallywith respect to the adjoining bearing surfaces.

In the present case, these protrusions are used such that clearanceangles, which are intended to ensure the necessary free-runningproperties of the cutting insert, are produced on the secondary cuttingedges. In other words, the clearance angles which are necessary for thefree-running properties of the cutting insert that are required duringmachining, are thus formed in the first and second protrusions. Thisoccurs essentially in that each protrusion has surfaces that are planarand/or of complex shape and are inclined with respect to the adjacentbearing surfaces and with respect to the adjacent secondary cuttingedges, such that in each case a plurality of clearance angles areproduced in the corners of the cutting insert. On account of thearrangement or formation of the clearance angles in these first andsecond protrusions, the cutting insert does not have to be excessivelytwisted on itself in order to effectively avoid a collision with thosecomponents of the cutting insert that are not used during machining.Otherwise, surfaces of much less complex shape arise as a result on theouter shell of the cutting insert, as is the case for example in thecutting insert known from EP 1 572 407 B1. This makes in particular themanufacture of the cutting insert easier and thus more cost-effective.

As a result of the first and second protrusions which are provided onthe secondary sides of each part and in which the clearance angles areintegrated, success has been had in preserving the symmetry propertiesof the cutting insert and nevertheless ensuring the free-runningproperties. The tangential cutting insert can thus be used in fourdifferent positions in the tool holder such that the four main cuttingedges are usable one after another without the cutting or geometricalproperties changing in the process.

A further central feature of the herein presented cutting insert isbased on the fact that the two main cutting edges of each part extendparallel to the two bearing surfaces of the in each case other part.This not only has a favorable effect on the symmetry properties of thecutting insert but also makes it possible to fix the cutting insertsecurely and in a mechanically stable position in a cutting insertreceptacle, provided for this purpose, on the tool holder. Such bearingsurfaces are frequently not configured parallel to the main cuttingedges or cutting edges in the case of the cutting inserts known from theprior art. This increases in particular the complexity of the insertseat and this in turn has a negative effect on manufacturing and to someextent even has a negative effect on the cutting or chip properties thatultimately arise during machining.

At this point it should be noted that the “center plane” used for thegeometrical description of the cutting insert is an imaginary auxiliaryplane which is not actually physically present.

Preferably, the cutting insert is substantially rhomboidal when viewedin plan view along the bore axis. Preferably, in particular the twoidentical, mutually opposite base surfaces of the cutting insert areeach configured in a planar manner and are substantially rhomboidal.

A “rhomboid” is understood to be a parallelogram which has four sides.The opposite sides of this parallelogram are in this case parallel andof equal length, wherein none of the four corners forms a right angle.However, the sum of all the corner angles is 360°. Such a rhomboid hastwo diagonals which have different lengths and intersect one anotherobliquely, that is to say not at right angles. A rhomboid thus differsfrom an equilateral rhombus.

However, it should be noted that the cutting insert is not exactlyrhomboidal in the described plan view. In particular, it differs atleast partially from the ideal shape of a rhomboid in the corners of thecutting insert. This is essentially on account of the first and secondprotrusions, already mentioned above, which project at the corners ofthe cutting insert. The base surfaces, which are preferably planar, alsodiffer slightly from the shape of a rhomboid. They are thus onlysubstantially rhomboidal.

The rhomboidal shape of the cutting insert having the first and secondprotrusions, which define the clearance angles, arranged thereon, hasthe advantage that in this way the required free-running and symmetryproperties can be realized in a favorable manner. As a result of thesubstantially rhomboidal shape of the cutting insert, relatively fewsurfaces of complex shape, which are difficult to manufacture, arise.The four main insert sides of the cutting insert can thus be identical.Similarly, only few inclined or convex surfaces have to be ground intothe cutting insert, thereby considerably lowering the machining outlayduring manufacturing.

According to a further refinement, one of the two-parts may be mappedonto the respective other part by rotation through 180° about a rotationaxis located in the center plane followed by rotation through a maincutting edge angle about the bore axis, wherein the described maincutting edge angle is an angle which the main cutting edges of one partenclose with the main cutting edges of the in each case other part.

Thus, the two parts are not mirror-inverted with regard to the centerplane. Rather, the two parts are geometrically and structurallyidentical parts-bodies which are in contact with one another along thecenter plane. The abovementioned coincidence relationship is intendedmerely to describe the spatial orientation thereof with respect to oneanother.

Overall, a cutting insert, the body of which has two opposite identicalbase surfaces and is delimited by four identical main insert surfacesthat extend between said base surfaces, is produced. Each of these maininsert surfaces has in each case a secondary side of the one part and amain side (including main cutting edge) of the other part. Opposite maininsert surfaces have in each case main cutting edges of the same part,whereas in the case of adjacent main insert surfaces, the main cuttingedge is arranged once at the lower rim and once at the upper rim of themain insert surface.

According to a further refinement, the first protrusions are configuredin a larger manner than the second protrusions. By contrast, both thefirst and second segmental cutting edges, that is to say the cornerradii or bevels, and the adjoining secondary cutting edges arepreferably configured to be the same size.

The reason for this resides in the free-running properties to bemaintained, that is to say in order to avoid collisions. Depending onthe milling application, it is thus possible, using the cutting insertaccording to this refinement, to cut via both corners (via bothsegmental cutting edges), or, in the case of tangential slot millingtools, in which a plurality of cutting inserts are axially offset withrespect to one another, the in each case protruding corner, on which thefirst segmental cutting edge is arranged (additionally brought about bythe larger first clearance angle), does not press in an undesired manneragainst the workpiece. This reduces flank wear.

According to a refinement, each first protrusion has in each case afirst flank which adjoins a first secondary cutting edge and creates afirst clearance angle at the respective first secondary cutting edge.Each second protrusion accordingly has a second flank which adjoins asecond secondary cutting edge and creates a second clearance angle atthe respective second secondary cutting edge. The first secondarycutting edges in each case adjoin the first segmental cutting edges. Thesecond secondary cutting edges in each case adjoin the second segmentalcutting edges. Preferably, the first flank is configured in a largermanner than the second flank and the first clearance angle in a largermanner than the second clearance angle. However, it goes without sayingthat the surface area of the first flank is only minimally larger thanthe surface area of the second flank.

The reasons for this reside once again in the required symmetryproperties and the free-running properties, which necessarily have to berealized, during the use of the cutting insert for machining.

The first and second clearance angles each prevent the remaining cuttingedges, not used during machining, or the corners of the cutting insertfrom colliding with the workpiece. The first and second clearance anglesmay be each in the range from 1° to 10°, preferably in the range from 1°to 5°.

On account of the cutting edge geometry selected for the cutting insert, when a workpiece is machined, what is referred to as a positive cut isproduced. The expression positive cut is used when chip removal takesplace via the rake face in the direction away from the decreasingmaterial (counter to the slot wall that arises during machining). Incontrast to the oppositely extending negative cut, such a positive cutis advantageous in terms of the chip-formation properties.

According to a further refinement, all four main cutting edges of thecutting insert are each at a first distance from the bore axis and allfour bearing surfaces of the cutting insert are each at a seconddistance from the bore axis, wherein the first distance is smaller thanthe second distance.

It goes without saying that the term “distance” is intended to beunderstood as meaning the perpendicular distance from the bore axis. Thebearing surfaces of a part thus project toward the front with respect tothe main cutting edges of the in each case other part; they are thusfurther away from the bore axis than the main cutting edges. Expressedthe other way round, the main cutting edges are offset further towardthe inside, in the direction of the central bore axis, with respect tothe bearing surfaces.

It is furthermore preferred for the main cutting edges to be at asmaller distance from the center plane than the base surfaces. The twomain cutting edges of each part are in this case each located in acommon main cutting edge plane (imaginary auxiliary plane) which extendsparallel to the center plane. As a result of this height offset betweenthe base surfaces and the two main cutting edges of the respective part,in each case a substantially planar main flank, which is inclined withrespect to the respective main cutting edge plane, arises between themain cutting edges of each part and the base surface of the same part.

This planar main flank is in turn necessary to ensure the requiredfree-running properties of the cutting insert, since otherwise the basesurfaces of the cutting insert could collide with the workpiece duringmachining. The inclination angle which the main flanks enclose with theadjoining base surface is preferably in the region of 5°.

Furthermore, the cutting insert preferably has a through-bore whichextends orthogonally to the base surfaces and breaks through the latter.This through-bore serves substantially for fastening the cutting insertin the tool holder. To this end, preferably a fastening means, inparticular a screw, is passed through this through-bore and fastened tothe tool holder.

Since the present disclosure relates not only to the cutting insertitself but also to the tool in which this cutting insert is used, thefollowing is mentioned finally in this regard: the cutting insert usedin the cutting-insert receptacle of the tool holder is, according to thepresent disclosure, arranged in a manner twisted through a definedcutting edge twist angle about a radial direction of the tool holdersuch that the main cutting edge used for machining encloses this cuttingedge twist angle with a plane which is defined by the radial directionand a rotation axis of the tool holder. The main cutting edge used formachining is thus, in other words, arranged in a manner rotated slightlywith respect to the machining or rotation direction of the milling tool.As a result, the cutting edge twist angle, which is also referred to asan axial angle on account of its arrangement, is produced.

The rotation of the indexable cutting insert or of the cutting insertwithin the tool holder has essentially the purpose of avoidingcollisions with the non-used cutting edges and also collisions with theabove-described first and second protrusions.

At this point, it should be noted that the use of the presented cuttinginsert is described primarily using the example of a tangential slotmilling tool. However, in principle, the presented cutting insert canlikewise also be used in end mills or in a turning holder. Therefore,the presented cutting insert is not limited to the application describedin the present case.

The above-mentioned features and those yet to be explained in thefollowing text are usable not only in the combination given in each casebut also in other combinations or on their own, without departing fromthe spirit and scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a first embodiment of a cuttinginsert according to the present disclosure,

FIG. 2 shows a plan view of the first embodiment of the cutting insertfrom above,

FIG. 3 shows a plan view of the first embodiment of the cutting insertfrom the front,

FIG. 4 shows a further plan view of the first embodiment of the cuttinginsert from the side,

FIG. 5 shows a sectional view of the first embodiment of the cuttinginsert (section B-B),

FIG. 6 shows a further sectional view of the first embodiment of thecutting insert (section A-A),

FIG. 7 shows a detail view from FIG. 6,

FIG. 8 shows a perspective view of a tool holder without the cuttinginsert inserted therein,

FIG. 9 shows a perspective view of the tool holder with the cuttinginsert inserted therein,

FIG. 10 shows a lateral plan view of the tool holder with an insertedcutting insert,

FIG. 11 shows a further lateral plan view of the tool holder with aninserted cutting insert, and

FIG. 12 shows a sectional view of the tool holder with an insertedcutting insert.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 to 6 show an embodiment of the cutting insert in various views,wherein the cutting insert is designated as a whole by the referencesign 10. It is clear from the perspective view illustrated in FIG. 1that it is in this case a four-edged indexable cutting insert 10 havingfour identical rectilinear main cutting edges 12 a-d (main cutting edge12 d illustrated in a concealed manner in FIG. 1, see in this regard forexample FIG. 3).

On account of its main use purpose, specifically tangential milling ortangential slot milling, this type of cutting insert 10 is also referredto as a tangential cutting insert. The external form of the cuttinginsert body is delimited by six sides: two end sides each comprising aplanar base surface 16 a, 16 b that is oriented orthogonally to a boreaxis 14 extending centrally through the cutting insert 10 (base surface16 b illustrated in a concealed manner in FIG. 1, see in this regard forexample FIGS. 5 and 6). Furthermore, the outer side of the cuttinginsert body is delimited by four identical main insert sides 18 a-d thatextend between the base surfaces 16 a, 16 b. A main cutting edge 12 a-dis arranged on each of these main insert sides 18 a-d, respectively.

It can likewise be seen in particular from FIG. 1 that the cuttinginsert 10 is constructed from two identical parts 20 a, b. The divisioninto the two parts 20 a, b is intended in the following text merely tosimplify the description of the cutting insert 10. However, this doesnot mean that there are in this case two separate components. However,dividing the cutting insert 10 into two identical parts 20 a, b appearsto be expedient in particular on considering FIG. 1. The two parts 20 a,b are connected along an imaginary center plane 11 which extendsorthogonally to the bore axis 14 and is at the same distance from eachof the two base surfaces 16 a, b. This center plane thus divides thecutting insert 10 in an imaginary manner into two identical parts, afirst part 20 a and a second part 20 b.

Each of these parts-bodies 20 a, b has two identical mutually opposingmain sides 22 a-d on which the main cutting edges 12 a-d are arranged,and two identical secondary sides 24 a-d that extend transverselythereto and are likewise opposite one another. The main sides 22 a and22 c are opposite one another and belong to the first part 20 a.Likewise, the secondary sides 24 b and 24 d that belong to the firstpart 20 a are located opposite one another. By contrast, the main sides22 b and 22 d and the secondary sides 24 a and 24 c belong to the secondpart 20 b.

Since each of the four identical main insert sides 18 a-d of the cuttinginsert 10 comprises a main side 22 a-d of one part 20 a, b and asecondary side 24 a-d of the other part 20 a, b, a 180° rotationalsymmetry of the cutting insert 10 is produced overall. The main insertside 18 a contains for example the main side 22 a of the upper part 20 aand the secondary side 24 a of the lower part 20 b. In the same way, themain insert side 18 b contains the secondary side 24 b of the upper part20 a and the main side 22 b of the lower part 20 b, etc.

On account of the four identical main insert sides 18 a-d and thealready mentioned properties of rotational symmetry through 180° of thecutting insert 10 about the bore axis 14, said cutting insert can thusbe used in four different positions in the tool holder without anychange occurring to the cutting geometry or the cutting properties. Forexample, first of all the main cutting edge 12 a could be used formachining. As soon as said main cutting edge 12 a becomes worn, thecutting insert 10 can be rotated through 180° about the bore axis 14such that the main cutting edge 12 c is then used. In order then toallow the two main cutting edges 12 b and 12 c to be used, the cuttinginsert merely has to be reversed about an axis located in the centerplane 11 and oriented orthogonally to the bore axis 14 and be fastenedin a corresponding manner to the tool holder again such that one of themain cutting edges 12 b, d is oriented toward the workpiece. It goeswithout saying that for this purpose the cutting insert 10 has to bedetached in each case from the tool holder and fastened again in its newposition.

The cutting insert 10 is fastened to the work holder preferably by afastening element, for example a screw, as is apparent from FIGS. 8 to12, which will be dealt with in more detail below. To this end, thisscrew can be inserted into the through-bore 26 introduced centrally intothe cutting insert 10. The through-bore 26 extends preferably exactlyorthogonally to the two base surfaces 16 a, b, that is to say along thebore axis 14. However, it goes without saying that other fasteningpossibilities are also readily conceivable, without departing from thescope of the present disclosure.

The cutting insert 10 comprises first protrusions 28 a-d and secondprotrusions 30 a-d arranged on each secondary side 24 a-d of the twoparts 20 a, b. The first and second protrusions 28 a-d and 30 a-d,respectively, of each secondary side 24 a-d are separated from oneanother in each case by a bearing surface 32 a-d located in the samesecondary side. The bearing surfaces 32 a-d are each configured in aplanar manner and extend orthogonally to the imaginary center plane 11,already mentioned above, which divides the cutting insert 10 into thetwo parts 20 a, b. If, for example, the secondary side 24 b, clearlyvisible in FIG. 1, of the upper part 20 a is taken into consideration,said secondary side 24 b has at its right-hand end, as illustrated inthe drawing, a first protrusion 28 b and at its left-hand end a secondprotrusion 30 a. The bearing surface 32 b extends in between. Theremaining secondary sides 24 a, 24 c and 24 d are also configured in thesame way.

Both the first protrusions 28 a-d and the second protrusions 30 a-dproject, as illustrated in the drawings, with respect to the bearingsurfaces 32 a-d from the respective secondary sides 24 a-d. They thusform a material elevation. As is furthermore visible in FIG. 1, theabovementioned symmetry properties of the cutting insert 10 are retainedon account of the alternate arrangement of the first and secondprotrusions 28 a-d and 30 a-d, respectively, in the end-side corners ofthe cutting insert 10.

The first and second protrusions 28 a-d and 30 a-d, respectively, createfirst and second segmental cutting edges 34 a-d and 36 a-d,respectively, which adjoin in each case the end of the rectilinear maincutting edges 12 a-d. Each main cutting edge 12 a-d thus transitionsinto a first segmental cutting edge 34 a-d at its respective first end38 a-d and into a second segmental cutting edge 36 a-d at its second end40 a-d. This is explained in more detail again in the present case byway of an example which is visible in particular in the top left-handpart of FIG. 1: the main cutting edge 12 a transitions into the firstsegmental cutting edge 34 a for example at its first end 38 a. Thisfirst segmental cutting edge 34 a is arranged on the first protrusion 28a. At the opposite end 40 a the main cutting edge 12 a transitions intothe second segmental cutting edge 36 a, which is arranged on the secondprotrusion 30 a. The first and second segmental cutting edges 34 a-d and36 a-d, respectively, are in each case configured either as corner radiior bevels. Since the workpiece can also be machined with these cornerradii or corner bevels, these are designated first and second segmentalcutting edges 34 a-d and 36 a-d, respectively, in the present case.

The two different types of protrusion 28 a-d and 30 a-d, respectively,preferably differ in shape and size. The two different types ofpart-cutting edges 34 a-d and 36 a-d are, by contrast, preferablyconfigured to be the same size.

Preferably, the first protrusions 28 a-d are configured to be largerthan the second protrusions 30 a-d. The different configuration in termsof geometry or size of the protrusions 28 a-d and 30 a-d, respectively,serves essentially to ensure the free-running properties, which arerelatively difficult to ensure on account of the complexity of thecutting insert structure, for the components and cutting edges that arenot used during the particular machining operation, and thus to avoidcollisions. In other words, the clearance angles that are necessary forthe free-running properties of the cutting insert 10 during machiningare formed directly in the first and second protrusions 28 a-d, 30 a-d.In the case of the cutting inserts of this type that are known from theprior art, these clearance angles are usually ensured by a relativelylarge twist of the cutting insert 10 on itself or by a cutting geometryof complex configuration. However, introducing the clearance angle, asproposed, into such nose-like protrusions 28 a-d, 30 a-d that project atthe corners of the cutting insert 10 can have advantages from amanufacturing point of view. Otherwise, the cutting insert 10 has alsoproved to be advantageous with regard to machining and chip-formingproperties.

As is apparent for example from the view illustrated in FIG. 2, theclearance angles created in the corners of the cutting insert 10 arerealized by first and second flanks 42 a-d and 44 a-d, respectively,provided on the first and second protrusions 28 a-d and 30 a-d,respectively. These first flanks 42 a-d are arranged in each case on thefirst protrusions 28 a-d. The second flanks 44 a-d, by contrast, arearranged on the second protrusions 30 a-d.

A first clearance angle produced at the first flanks 42 a-d isdesignated angle a in FIG. 2. FIG. 2 likewise shows a second clearanceangle β produced at the second flanks 44 a-d. In FIG. 2, the secondclearance angle β is illustrated only schematically, however, since,according to the embodiment illustrated here, it has a size of 0°.However, other angle sizes are also conceivable in principle.Preferably, both the first clearance angle a and the second clearanceangle β are selected to be in the range from 0 to 10°, in particular inthe range from 0 to 5°.

In order to ensure the free-running properties, it is particularlypreferred for the first clearance angle α to be larger than the secondclearance angle β. It goes without saying that these clearance angles α,β change anyway, depending on the orientation of the cutting insert 10in the tool holder. In the case of a cutting insert that is arranged inthe tool holder in a slightly twisted manner at an axial angle γ₂, as isillustrated by way of example in FIG. 11, the size of the two radialclearance angles α and β changes anyway such that the angle α₁ indicatedin FIG. 11 is smaller than the angle α illustrated in FIG. 2 and theangle β₁ illustrated in FIG. 11 is larger than the angle β illustratedin FIG. 2.

Otherwise, the first and second flanks 42 a-d and 44 a-d, respectively,are also inclined with respect to the bore axis 14 (and thus are notparallel thereto), with the result that in particular the furtherclearance angle δ illustrated in FIG. 10 is produced. Thus, undesiredcollisions with the remaining components of the cutting insert 10 do notoccur either in the axial or in the radial direction.

As is apparent in particular from the plan view illustrated in FIG. 2,the cutting insert 10 is substantially rhomboidal in plan view. Inparticular, the end-side base surfaces 16 a, b of each part 20 a, b arerhomboidal. It goes without saying that neither the cutting insert 10 asa whole nor the base surfaces 16 a, b correspond exactly to a rhomboid,but are substantially similar to this shape. In addition to the parallelproperties of opposite sides, substantially the characteristic featureof a rhomboid is met in the present case, namely that adjacent sidesenclose an angle of ≠90° with one another. As is apparent from FIG. 2,for example the main cutting edge 12 a encloses an angle ε of less than90° with the bearing surface 32 b. Preferably, this angle ε is in theregion of 80°.

A further central feature of the cutting insert 10 is that the maincutting edges 12 a-d of the one part 20 a, b extend parallel to thebearing surfaces 32 a-d of the in each case other part 20 a, b. As canbe gathered for example from FIG. 2, the main cutting edge 12 a of thepart 20 a extends parallel to the bearing surface 32 a of the part 20 b.In the same way, the main cutting edge 12 c of the part 20 a alsoextends parallel to the bearing surface 32 c of the part 20 b. It canadditionally be gathered both from FIG. 2 and from FIG. 5 that the maincutting edges 12 a-d are offset toward the inside, in the direction ofthe central bore axis 14, with respect to the bearing surfaces 32 a-d.Thus, in other words, the bearing surfaces 32 a-c are at a greaterdistance from the bore axis 14 than the main cutting edges 12 a-c.

Furthermore, the main cutting edges 12 a-d are also slightly verticallyoff-set with respect to the base surfaces 16 a, b (see for example FIG.4). Specifically, the distance of the main cutting edges 12 a-d from thecenter plane 11 is smaller than the distance of the base surfaces 16 a,b from this center plane 11. On account of this vertical offset, mainflanks 46 a, d are therefore produced in each case between the maincutting edges 12 a-d and the base surfaces 16 a, b of the same part 20a, b.

FIG. 7 illustrates in an enlarged manner the respective clearance angleτ₁ produced by the main flanks 46 a-d using the example of the mainflank 46 a. This angle may be in the range from 0.5 to 10°, inparticular in the region of 5° or exactly 5°. Furthermore, it can begathered from the enlarged view illustrated in FIG. 7 that in each casea rake face 48 a-d, via which the chip produced during machining can runoff, adjoins each main cutting edge 12 a-d on the associated main side18 a-d. By way of these rake faces 48 a-d that are inclined relative tothe bore axis 14, preferably a rake angle τ₂ in the range from 0 to 40°,preferably in the range from 15° to 25°, or in particular of exactly22°, is produced.

FIGS. 8 to 12 show by way of example a tool, in which the cutting insert10 is typically used. The tool is designated as a whole by the referencesign 100 in these figures.

The tool illustrated by way of example is illustrated in this case as atypical tangential milling tool 100. This tangential milling tool 100has a tool holder 50 which is configured so as to be rotationallysymmetrical about a rotation axis 52. At least one, preferably amultiplicity of cutting insert receptacles 54 (illustrated in detail inFIG. 8), which act as a receptacle for in each case one cutting insert10, are provided on the circumference of the tool holder 50. In FIGS. 9to 12, by way of example in each case one cutting insert 10 is inserted.This cutting insert 10 is preferably fastened releasably to the toolholder 50 by way of a screw 56.

The structural details of the cutting insert receptacle 54 are apparentfrom FIG. 8. The cutting insert receptacle 54 has in each case bearingsurfaces 58 and 60 at which the cutting insert 10 rests against the toolholder 50 by way of its bearing surfaces 32 a-d. A further base surface62 arranged in the base of the cutting insert receptacle 54 serves as abearing surface against which the cutting insert 10 rests by way of oneof its end-side base surfaces 16 a, b. The bearing surfaces 58 and 60are preferably configured orthogonally to the base surface 62. In thisway, a mechanically stable and clearly defined insert seat is realized.

FIG. 11 illustrates once again the arrangement of the cutting insert 10within the tool holder 50. It is apparent therefrom that the cuttinginsert 10 is arranged in the tool holder 50 in a manner twisted throughan angle γ₂ about its bore axis. This angle γ₂ is also designated axialangle. More specifically, this is the angle which the main cutting edge12 a used for machining encloses with the axial direction of the toolholder 50. On account of the angle E and the small twist angle in theaxial direction γ₁ (see for example FIG. 2), a (relatively) large axialangle γ₂ (γ₁<γ₂) is produced. A large axial angle y₂ is desired in thisdesign in order to achieve a cut that is as positive (smooth) aspossible. The contour deviation (deviation of the cutting contourproduced on the workpiece from the cutting edge contour of the cuttinginsert) is not in the foreground in this type of cutting insert, butshould not be too large.

It is also apparent from FIG. 10 that a further clearance angle δ, whichguarantees radial free running, is produced by the flanks 44 a-d formedin the protrusions 30 a-d.

For the sake of completeness, it should also be mentioned that FIG. 12illustrates the section A-A indicated in FIG. 11.

In summary, it can thus be stated that the inventors have succeeded inproviding an alternative four-edged tangential cutting insert which, onaccount of its relatively simply configured cutting edge geometry, iseasy and cost-effective to manufacture and nevertheless has highmachining accuracy. The clearance angles that are required forfree-running properties are formed by what are referred to as “noses”which are designated protrusions in the present case. As a result, it ispossible to machine the workpiece even with the cutting-edge cornerswithout undesired collisions.

What is claimed is:
 1. A cutting insert for a tool for machining aworkpiece, comprising: two identical parts, wherein each part has a basesurface, two identical mutually opposite main sides and two identicalmutually opposite secondary sides, and wherein the base surface of theone of the two parts is opposite and parallel to the base surface of theother one of the two parts; four rectilinear main cutting edges, whereineach of the two parts comprises two of the four rectilinear main cuttingedges; four first segmental cutting edges, wherein each of the two partscomprises two of the four first segmental cutting edges; four secondsegmental cutting edges, wherein each of the two parts comprises two ofthe four second segmental cutting edges; a through-bore having a boreaxis which extends perpendicularly and centrally through the two basesurfaces; wherein the cutting insert has a 180° rotational symmetryabout the bore axis, wherein the two identical parts are connected toeach other along a center plane which extends orthogonally to the boreaxis and has the same distance from each of the two base surfaces,wherein the four main cutting edges extend parallel to the center plane,wherein each main side comprises one of the four main cutting edges,wherein the two main cutting edges of each part extend parallel to oneanother and transversely to the two main cutting edges of the respectiveother part, and wherein each main cutting edge transitions at itsrespective first end into one of the four first segmental cutting edgesand at its respective second end, opposite the first end, into one ofthe four second segmental cutting edges, wherein each secondary sidecomprises (i) a planar bearing surface which extends orthogonally to thecenter plane, (ii) a first protrusion on a first side of the planarbearing surface and (iii) a second protrusion on a second side of theplanar bearing surface, wherein the first and the second protrusionseach adjoin the bearing surface arranged on the respective samesecondary side and project with respect to said bearing surface, whereineach of the first segmental cutting edges is arranged on one of thefirst protrusions and each of the second segmental cutting edges isarranged on one of the second protrusions, and wherein the bearingsurfaces of each part extend parallel to the main cutting edges of therespective other part.
 2. The cutting insert as claimed in claim 1,wherein the cutting insert has exactly four identical main cuttingedges.
 3. The cutting insert as claimed in claim 1, wherein the cuttinginsert is substantially rhomboidal when viewed in plan view along thebore axis.
 4. The cutting insert as claimed in claim 1, wherein the twoidentical, mutually opposite base surfaces of the cutting insert areeach planar and substantially rhomboidal.
 5. The cutting insert asclaimed in claim 1, wherein one of the two parts of the cutting insertmay be mapped onto the respective other part of the cutting insert (i)by rotation through 180° about a rotation axis located in the centerplane followed (ii) by rotation through a main cutting edge angle aboutthe bore axis, wherein the main cutting edge angle is an angle which themain cutting edges of one part enclose with the main cutting edges ofthe respective other part.
 6. The cutting insert as claimed in claim 1,wherein the first protrusions are larger than the second protrusions. 7.The cutting insert as claimed in claim 1, wherein each of the firstprotrusions has a first flank which adjoins a first secondary cuttingedge and creates a first clearance angle at the respective firstsecondary cutting edge.
 8. The cutting insert as claimed in claim 1,wherein each of the second protrusions has a second flank which adjoinsa second secondary cutting edge and creates a second clearance angle atthe respective second secondary cutting edge.
 9. The cutting insert asclaimed in claim 1, wherein each of the first protrusions has a firstflank which adjoins a first secondary cutting edge and creates a firstclearance angle at the respective first secondary cutting edge, whereineach of the second protrusions has a second flank which adjoins a secondsecondary cutting edge and creates a second clearance angle at therespective second secondary cutting edge, wherein the first flank islarger than the second flank, and wherein the first clearance angle islarger than the second clearance angle.
 10. The cutting insert asclaimed in claim 1, wherein the main cutting edges are each at a firstdistance from the bore axis and the bearing surfaces of the cuttinginsert are each at a second distance from the bore axis, and wherein thefirst distance is smaller than the second distance.
 11. The cuttinginsert as claimed in claim 1, wherein the main cutting edges are at asmaller distance from the center plane than the base surfaces.
 12. Thecutting insert as claimed in claim 1, wherein the main cutting edges ofeach part are located in a respective common main cutting edge planewhich extends parallel to the center plane, and wherein a substantiallyplanar main flank is provided locally in between each of the two maincutting edges of each part and the base surface of the same part,respectively, each main flank being inclined with respect to therespective main cutting edge plane of the same part.
 13. A tool formachining a workpiece, in particular for tangential milling, having atool holder which has at least one cutting-insert receptacle in which acutting insert is releasably fastened, the cutting insert comprising:two identical parts, wherein each part has a base surface, two identicalmutually opposite main sides and two identical mutually oppositesecondary sides, and wherein the base surface of the one of the twoparts is opposite and parallel to the base surface of the other one ofthe two parts; four rectilinear main cutting edges, wherein each of thetwo parts comprises two of the four rectilinear main cutting edges; fourfirst segmental cutting edges, wherein each of the two parts comprisestwo of the four first segmental cutting edges; four second segmentalcutting edges, wherein each of the two parts comprises two of the foursecond segmental cutting edges; a through-bore having a bore axis whichextends perpendicularly and centrally through the two base surfaceswherein the cutting insert has a 180° rotational symmetry about the boreaxis, wherein the two identical parts are connected to each other alonga center plane which extends orthogonally to the bore axis and has thesame distance from each of the two base surfaces, wherein the four maincutting edges extend parallel to the center plane, wherein each mainside comprises one of the four main cutting edges, wherein the two maincutting edges of each part extend parallel to one another andtransversely to the two main cutting edges of the respective other part,and wherein each main cutting edge transitions at its respective firstend into one of the four first segmental cutting edges and at itsrespective second end, opposite the first end, into one of the foursecond segmental cutting edges, wherein each secondary side comprises(i) a planar bearing surface which extends orthogonally to the centerplane, (ii) a first protrusion on a first side of the planar bearingsurface and (iii) a second protrusion on a second side of the planarbearing surface, wherein the first and the second protrusions eachadjoin the bearing surface arranged on the respective same secondaryside and project with respect to said bearing surface, wherein each ofthe first segmental cutting edges is arranged on one of the firstprotrusions and each of the second segmental cutting edges is arrangedon one of the second protrusions, and wherein the bearing surfaces ofeach part extend parallel to the main cutting edges of the respectiveother part.
 14. The tool as claimed in claim 13, wherein the tool holderis symmetrical about a rotation axis, and wherein the at least onecutting insert is arranged in the cutting-insert receptacle in a mannertwisted through a defined cutting edge twist angle about a radialdirection of the tool holder such that the main cutting edge used formachining encloses this cutting edge twist angle with a plane which isdefined by the radial direction and the rotation axis of the toolholder.
 15. A cutting insert for a tool for machining a workpiece,wherein the cutting insert has a 180° rotational symmetry about a boreaxis extending perpendicularly and centrally through two opposing,identical base surfaces of the cutting insert, and has two identicalparts which are connected along a center plane, wherein said centerplane extends orthogonally to the bore axis and has the same distancefrom each of the two base surfaces, wherein each part has two identicalmutually opposite main sides and two identical mutually oppositesecondary sides, wherein each main side has a rectilinear main cuttingedge extending parallel to the center plane, and each secondary side hasa planar bearing surface extending orthogonally to the center plane,wherein the two main cutting edges of each part extend parallel to oneanother and transversely to the two main cutting edges of the respectiveother part, and wherein the two main cutting edges of each part extendparallel to the two bearing surfaces of the respective other part,wherein each main cutting edge transitions at its respective first endinto a first segmental cutting edge which is arranged on a firstprotrusion provided on an adjacent secondary side of the respectivepart, and wherein each main cutting edge transitions into a secondsegmental cutting edge at its respective second end, opposite the firstend, which is arranged on a second protrusion provided on the respectiveother adjacent secondary side of the respective part, wherein the firstand the second protrusions each adjoin the bearing surface arranged onthe respective same secondary side and project with respect to therespective bearing surface.